From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6800FC433B4 for ; Wed, 21 Apr 2021 14:29:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2F6EC61459 for ; Wed, 21 Apr 2021 14:29:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243563AbhDUO3h (ORCPT ); Wed, 21 Apr 2021 10:29:37 -0400 Received: from mx2.suse.de ([195.135.220.15]:39110 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238173AbhDUO3f (ORCPT ); Wed, 21 Apr 2021 10:29:35 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1619015341; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=vb4w4rQjHd7BOri6tnIw9XpvN8SwPbJF3toyQYgzGRg=; b=qYNAOXNH2YsGh7mAvqkzXGBRCliQc8swtDatbLoWNIYm4Q4oFYaMdsxs2xgIFTxRiGYjzy e+teDibROzLugbdHxvDdxHVKbGaJEQ6PDxt85RVPy2LqF/PlbQe6QsddxC6D1vCcBoxuds iBtliyQaR6FGnV5opOHT+yreCfUKFG8= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 3900EAF65; Wed, 21 Apr 2021 14:29:01 +0000 (UTC) Date: Wed, 21 Apr 2021 16:29:00 +0200 From: Michal Hocko To: Shakeel Butt Cc: Johannes Weiner , Roman Gushchin , Linux MM , Andrew Morton , Cgroups , David Rientjes , LKML , Suren Baghdasaryan , Greg Thelen , Dragos Sbirlea , Priya Duraisamy Subject: Re: [RFC] memory reserve for userspace oom-killer Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 21-04-21 06:57:43, Shakeel Butt wrote: > On Wed, Apr 21, 2021 at 12:16 AM Michal Hocko wrote: > > > [...] > > > To decide when to kill, the oom-killer has to read a lot of metrics. > > > It has to open a lot of files to read them and there will definitely > > > be new allocations involved in those operations. For example reading > > > memory.stat does a page size allocation. Similarly, to perform action > > > the oom-killer may have to read cgroup.procs file which again has > > > allocation inside it. > > > > True but many of those can be avoided by opening the file early. At > > least seq_file based ones will not allocate later if the output size > > doesn't increase. Which should be the case for many. I think it is a > > general improvement to push those who allocate during read to an open > > time allocation. > > > > I agree that this would be a general improvement but it is not always > possible (see below). It would be still great to invest into those improvements. And I would be really grateful to learn about bottlenecks from the existing kernel interfaces you have found on the way. > > > Regarding sophisticated oom policy, I can give one example of our > > > cluster level policy. For robustness, many user facing jobs run a lot > > > of instances in a cluster to handle failures. Such jobs are tolerant > > > to some amount of failures but they still have requirements to not let > > > the number of running instances below some threshold. Normally killing > > > such jobs is fine but we do want to make sure that we do not violate > > > their cluster level agreement. So, the userspace oom-killer may > > > dynamically need to confirm if such a job can be killed. > > > > What kind of data do you need to examine to make those decisions? > > > > Most of the time the cluster level scheduler pushes the information to > the node controller which transfers that information to the > oom-killer. However based on the freshness of the information the > oom-killer might request to pull the latest information (IPC and RPC). I cannot imagine any OOM handler to be reliable if it has to depend on other userspace component with a lower resource priority. OOM handlers are fundamentally complex components which has to reduce their dependencies to the bare minimum. > [...] > > > > > > I was thinking of simply prctl(SET_MEMPOOL, bytes) to assign mempool > > > to a thread (not shared between threads) and prctl(RESET_MEMPOOL) to > > > free the mempool. > > > > I am not a great fan of prctl. It has become a dumping ground for all > > mix of unrelated functionality. But let's say this is a minor detail at > > this stage. > > I agree this does not have to be prctl(). > > > So you are proposing to have a per mm mem pool that would be > > I was thinking of per-task_struct instead of per-mm_struct just for simplicity. > > > used as a fallback for an allocation which cannot make a forward > > progress, right? > > Correct > > > Would that pool be preallocated and sitting idle? > > Correct > > > What kind of allocations would be allowed to use the pool? > > I was thinking of any type of allocation from the oom-killer (or > specific threads). Please note that the mempool is the backup and only > used in the slowpath. > > > What if the pool is depleted? > > This would mean that either the estimate of mempool size is bad or > oom-killer is buggy and leaking memory. > > I am open to any design directions for mempool or some other way where > we can provide a notion of memory guarantee to oom-killer. OK, thanks for clarification. There will certainly be hard problems to sort out[1] but the overall idea makes sense to me and it sounds like a much better approach than a OOM specific solution. [1] - how the pool is going to be replenished without hitting all potential reclaim problems (thus dependencies on other all tasks directly/indirectly) yet to not rely on any background workers to do that on the task behalf without a proper accounting etc... -- Michal Hocko SUSE Labs